WASHINGTON _ Forty years ago this Saturday, President Lyndon Johnson signed the Voting Rights Act of 1965 into law, bolstering the right of blacks to vote in states where it had been denied or suppressed.

Today, Southern politics have been transformed in two fundamental ways: Blacks exercise power and hold office in great numbers, and Republicans, with almost no black support, are the dominant party.

The two are not unrelated. Republican gains came partly through creation of black districts, which improved GOP prospects in surrounding districts “bleached” of blacks, who reliably vote Democratic.

The VRA’s key provisions expire in 2007. And with Congress facing a vote on reauthorization, the topsy-turvy politics of voting rights are coming to a head.

In 2003, in Georgia v. Ashcroft, the Supreme Court ruled _ over the objections of the Bush Justice Department _ that the state’s Democrat-controlled Legislature did not violate the VRA in drawing up a state Senate redistricting plan that spread black voters out a bit.

The court’s conservatives said black political interests were better served with more Democratic districts, even if this risked electing fewer blacks. In the past, the federal government had used the VRA to reject any plan that reduced the concentration of blacks in districts where they were the majority. There was to be no backsliding.

Writing for the majority in a 5-4 decision, Justice Sandra Day O’Connor remarked that she was particularly moved by Rep. John Lewis’ testimony in favor of the redistricting plan. Lewis, hero of the bloody battle for voting rights in Selma, Ala., that precipitated passage of the VRA, was elected to Congress from a black district in Atlanta in 1986.

Now the nation’s civil rights leadership _ as represented by the Leadership Conference on Civil Rights, the NAACP Legal Defense and Educational Fund, and others _ wants to limit the impact of Georgia v. Ashcroft. They argue that the premium should be placed on whether minority voters can elect candidates of their race, not merely candidates of their party.

This requires the Democrats, the civil rights movement’s staunchest allies, to spurn a court decision that seemed a gift.

Section 5 of the VRA requires places with a history of discrimination _ all of Alabama, Georgia, Louisiana, Mississippi, South Carolina and Texas; parts of Virginia and North Carolina; and all or part of a few other states _ to get federal approval before altering voting practices or procedures, redistricting included. It was this process that ultimately brought the Georgia plan to the nation’s highest court.

The iconic leader of the reauthorization drive in Congress is none other than Rep. Lewis, who wants to rewrite Section 5 to restore the pre-Georgia v. Ashcroft interpretation of the law. “I think we’ve got to find some balance, some happy medium,” he said.

He is in the unusual position of asking colleagues to correct a Supreme Court opinion that lionizes his own longing for “an all-inclusive community, where we would be able to forget about race and color and see people as people, as human beings, just as citizens.”

But his logic is that the court provided local officials with leeway that a less-enlightened jurisdiction might misuse. “I believe that there is the strong possibility that in certain states, certain counties and certain political districts, they would return to the dark past,” he said.

Meanwhile, Republicans face their own predicament.

Resist the reauthorization, or merely a stronger Section 5, and they risk inflaming minority voters _ all to gut a law that has proved useful in running up GOP majorities in the South. They hand the Democrats an issue in the 2006 midterm elections, even as they themselves try to get right with black voters. Go along, and they betray segments of their white base who bristle that, after four decades and a world of change, Section 5 still singles out the South for special scrutiny.

“I just don’t see the need for it,” said U.S. Rep. Lynn Westmoreland, R-Ga.

He pointed out that Georgia’s attorney general, labor commissioner and three of its state Supreme Court justices, including the chief justice _ all of whom are elected _ are black. Two of its four black members of Congress _ Sanford Bishop and David Scott _ are from majority white districts.

“We are supposed to be one nation, and if we are going to have (Section 5), it ought to apply to all 50 states,” Westmoreland said.

But Debo Adegbile, associate director of litigation for the NAACP Legal Defense and Educational Fund, said making Section 5 national _ or permanent, as some Republicans suggest _ would be an unconstitutional overreach, setting it up for fatal challenge before the Supreme Court.

All this accumulated irony reflects the contending ways in which the South has changed since President Johnson signed the law.

In a chapter for a forthcoming book on the VRA, David Bositis, an expert on black politics with the Joint Center for Political and Economic Studies, notes that while the number of black elected officials grew more than tenfold after 1965, “this advancement … has been accompanied by an even greater advancement of the views and interests of the class of people who were most opposed to the passage of the Voting Rights Act _ namely, conservative Southern whites.”

How much black districts are at fault for the demise of white Democrats is a matter of bitter debate.

At a recent Washington conference on the act, Laughlin McDonald, director of the Atlanta-based ACLU Voting Rights Project, noted that the VRA was intended to empower minority communities, not the Democratic Party. Many in the civil rights community think white Democrats blithely blame minority districts for their own failures.

But Edward Blum, a fellow with the Washington-based Center for Equal Opportunity, and a longtime crusader against race-conscious public policy, said Democrats and their allies fool themselves if they underestimate how much racial districting has cost them, and what a blunder it would be for them to override Georgia v. Ashcroft.

“They would truly be digging their own grave for control of legislative bodies really for the next generation,” Blum said. “It is highly unlikely Democrats would be able to regain control of the U.S. House or any of the legislative bodies in any of the covered Deep South.”

No group has more at stake than black members of Congress. All of them are Democrats. Many have considerable seniority and would wield great power if the Democrats regained control of the House.

“Section 5 ought to be allowed to gracefully expire in 2007,” said Vanderbilt University political scientist Carol Swain, whose book “Black Faces, Black Interests” was cited in Georgia v. Ashcroft as evidence that simply electing more minority representatives may not maximize the influence of minority voters.

But, Swain said, “Apparently black members of Congress have grown comfortable with being in the minority. Otherwise, why would they endorse a strategy that works against the long-term interests of their party?”

Some members of the Black Caucus are treading lightly.

A spokesman for U.S. Rep. Robert Scott, D-Va., said that while the congressman was intrigued by the question of reworking Section 5, he was not yet prepared to talk about it.

And U.S. Rep. Artur Davis, D-Ala., a moderate whose district includes Selma and Birmingham, said that while he has not looked closely at Georgia v. Ashcroft, he was open to strengthening Section 5, but thought the bipartisan consensus may be to reauthorize the provision as is.

Ultimately, a reauthorized VRA will be tested in the courts, and both sides are laying the groundwork.

Civil rights groups are combing the covered territories for evidence of abuses that warrant continuing Section 5. Blum is collecting data to prove that white voters in the South are as likely to vote for black candidates as are white voters in the rest of America, rendering Section 5 obsolete and unfair.

But Bositis said it is still easy, for example, to distinguish Mississippi, which has never elected a black candidate statewide, from Illinois, which has on several occasions _ most recently in sending Barack Obama to the U.S. Senate.

And state Sen. Robert Brown, a black Democrat from Macon instrumental in the redistricting at issue in Georgia v. Ashcroft, like Lewis supports a stronger Section 5 _ precisely because he is not sure black candidates could fare as well with white voters elsewhere in the South.